1. Field of the Invention
The present invention relates to a fuel cell stack including a box-shaped casing and a stack body provided in the casing. The stack body is formed by stacking a plurality of unit cells. Each of the unit cells includes an electrolyte electrode assembly and separators sandwiching the electrolyte electrode assembly. The electrolyte electrode assembly includes a pair of electrodes, and an electrolyte interposed between the electrodes.
2. Description of the Related Art
For example, a solid polymer fuel cell employs a membrane electrode assembly which includes an anode, a cathode, and an electrolyte membrane (electrolyte) interposed between the anode and the cathode. The electrolyte membrane is a polymer ion exchange membrane. The membrane electrode assembly and separators sandwiching the membrane electrode assembly make up a unit of a fuel cell (unit cell) for generating electricity.
In the fuel cell, a fuel gas such as a gas chiefly containing hydrogen (hereinafter also referred to as the “hydrogen-containing gas”) is supplied to the anode. A gas chiefly containing oxygen or air (hereinafter also referred to as the “oxygen-containing gas”) is supplied to the cathode. The catalyst of the anode induces a chemical reaction of the fuel gas to split the hydrogen molecule into hydrogen ions and electrons. The hydrogen ions move toward the cathode through the electrolyte membrane, and the electrons flow through an external circuit to the cathode, creating a DC electrical energy.
Generally, a predetermined number of, e.g., several tens to several hundreds of fuel cells are stacked together to form a fuel cell stack for achieving the desired level of electricity in power generation. Components of the fuel cell stack need to be tightened together reliably under pressure so that the internal resistance of the fuel cell does not increase, and the sealing performance for preventing leakage of reactant gases is maintained.
In this regard, for example, a fuel cell stack disclosed in Japanese Laid-Open Patent Publication No. 2002-298901 is known. The fuel cell stack includes a stack body formed by stacking a predetermined number of unit cells. Current collecting electrodes (terminal plates) are provided outside the stack body. Further, end plates are stacked on the outside of the terminal plates. The end plates are joined to the casing by hinge mechanisms. The casing includes a plurality of panels (side plates) provided on upper, lower, left, and right sides between the end plates.
Thus, in the conventional technique, the number of components is reduced effectively, and it is possible to use thin end plates. It is possible to reduce the size and the weight of the entire fuel cell stack easily.
In the conventional technique, for example, as shown in FIG. 7, at longitudinal opposite ends of a panel 1 of the casing, a plurality of cylindrical insertion portions 4a to 4c are provided. Coupling pins 3 of hinge mechanisms 2 are inserted in the insertion portions 4a to 4c at the opposite ends of the panel 1. At this time, typically, the insertion portions 4a to 4c are joined to the opposite ends of a surface member 5 of the panel 1 by laser welding or the like.
However, since the insertion portions 4a to 4c are joined to the ends of the surface member 5 individually, it is considerably difficult to form insertion holes 6a to 6c of the insertion portions 4a to 4c coaxially, i.e., in alignment with each other. If the insertion holes 6a to 6c are not in alignment with each other, the coupling pin 3 cannot be inserted into the insertion holes 6a to 6c. Thus, the assembling operation of the hinge mechanism 2 cannot be performed efficiently. Further, when a load is applied to the casing, a bending moment is applied to the panel 1, and the strength of the hinge mechanism 2 is lowered.